This invention relates to coffee and more particularly to the production of a high quality coffee extract.
The commercial manufacture of coffee extract is achieved via the well-known process of percolation. Percolation is the semi-continuous, counter-current extraction of soluble coffee solids from roasted and ground coffee with an aqueous extraction liquid. A percolator set, generally comprised of from 4 to 8 extraction columns is normally employed in such a process.
At steady-state operation, the extraction columns of the percolator set contain roasted and ground coffee of varying degrees of extraction. The most extracted coffee is contained in the "spent stage" extraction column and the roasted and ground coffee in successive columns is progressively less extracted (fresher). The least extracted coffee, generally fresh or unextracted roasted and ground coffee, is contained in the "fresh stage" extraction column.
Aqueous extraction liquid, generally water, is heated and fed continuously to and through the spent stage extraction column. The aqueous extraction liquid initially solubilizes the soluble coffee solids contained in the roasted and ground coffee and then extracts these solids from the coffee bed. The aqueous extraction liquid exiting the spent stage, now containing a minor amount of soluble coffee solids, is then passed to and through the next successive extraction column in the percolator set, containing the next most extracted coffee, extracts soluble solids therefrom and is then passed through the next successive extraction column. In like manner the aqueous extraction liquid passes through the remaining extraction columns contacting the progressively fresher coffee contained therein, the aqueous extraction liquid thereby becoming more highly concentrated in soluble coffee solids.
After passing through the extraction column containing the least extracted coffee (the fresh stage), a pre-determined portion of the aqueous extraction liquid is drawn off from the fresh stage as coffee extract. This coffee extract is then further processed to produce a soluble coffee product.
To begin a new cycle, the spent stage extraction column is taken off-stream and aqueous extraction liquid is fed to the spent stage for this cycle, the roasted and ground coffee contained therein being the next most extracted coffee from the previous cycle, and the extraction liquid is passed through the successive extraction columns contacting the progressively fresher coffee contained therein and extracting soluble solids therefrom. An extraction column containing freshly roasted and ground coffee is placed on-stream thus becoming the fresh stage for coffee extract draw-off for this cycle.
In like manner, successive cycles are continued. A given bed of roasted and ground coffee, therefore, becomes progressively more extracted in each succeeding cycle as it moves in a batch manner counter-current to the continuous flow of extraction liquid.
A unique feature of coffee percolation is the desirability of preserving to the highest possible degree the characteristic flavor and aroma of roasted and ground coffee. As in nearly all extraction operations, economic considerations make it desirable to maximize the yield of soluble coffee solids obtained from a given charge of roasted and ground coffee. Similarly, it is desirable to obtain economical concentrations of soluble coffee solids in the drawn-off coffee extract so as to lessen the water removal requirements needed during drying to a final soluble coffee product. However, these economic considerations must necessarily be balanced against the desire to obtain a flavorful coffee extract similar to that obtained when roasted and ground coffee is home-brewed. Thus, typical extraction techniques such as high temperature processing, while effective in obtaining relatively high yields, have a pronounced detrimental effect on the delicate flavor and aroma components of coffee.
It is common in the coffee industry today to compromise those objectives by resorting to relatively high temperature treatment in the spent stage and the next few successive stages to generate autoclaved or hydrolyzed coffee solids to improve the overall yield of the extraction process. The extraction liquid is then cooled (through either natural cooling or suitable heat exchange apparatus) before contacting the coffee in the fresher stages of the percolator set. While effective in producing economical yields it is still found that the resulting coffee extract drawn off from the fresh stage is somewhat lacking in the characteristic flavor of home-brewed roasted and ground coffee. More particularly, it is extremely desirable to achieve highly efficient extraction of soluble coffee solids in the fresher stages since these columns contain the roasted and ground coffee having the most flavorful and aromatic coffee solids. If these coffees are inefficiently extracted, they will be subjected to more severe extraction conditions as they move "back" in the percolator set (i.e., as they become progressively more extracted in succeeding cycles). The result is that valuable, flavorful coffee solids are lost through degradation. The resulting coffee extract, while produced at economical yield and concentrations, may therefore still be lacking in high quality flavor and aroma notes.
It is accordingly the primary object of this invention to produce a high quality coffee extract at commercially economical yields and concentrations.
This and other objects will become more apparent upon reading the specification and claims which follow.